Cocoa would be a good start.
Congrats on your pre-engagement!
Since you're not interested in a traditional wedding, you could go to the courthouse and sign the documents with important people (family, special friends) as witnesses, and then go to your grandma's for a massive potluck. You provide the roast animal (and probably the cake), and have your guests bring a dish of whatever. Cheap, fun, memorable!
My wedding shindig- should I have one- has evolved to the point of telling people to bring tents for camping out in my parent's yard for the weekend.
Oh! For my mom's cousin's second wedding they did a period wedding- and asked all the guests to come in costume! Mom had a blast planning her late 1800s costume